This invention relates to an apparatus and method for electrostatic loading of a drug onto an implantable medical device such as a stent.
FIG. 1 illustrates a stent 10 having a conventional design of struts 12 interconnected by connecting elements 14. Struts 12 and connecting elements 14 are separated by gaps 16. Stent 10 is generally cylindrical and radially compressible. Compressible embodiments of stent 10 can be balloon expandable or self-expandable. Although stents work well mechanically, the chronic issues of restenosis and, to a lesser extent, thrombosis remain a significant clinical problem. These events are affected and made worse by the degree of injury and the hemodynamic disturbance caused by the stent. In order to more effectively treat these conditions, pharmacological therapy can be used in conjunction with stent therapy. Maintaining the necessary drug concentration at the lesion site for the necessary period of time remains a challenge, however. This can be done with brute force methods using oral or intravenous administration but the issues of systemic toxicity and side effects arise. Therefore, a preferred route can be achieved by local delivery of drug from the stent itself.
Being made of metal, plain stents are not useful for drug delivery. To serve as a drug reservoir, a coating, usually of a polymer, is applied by dipping or spraying the stent. A solution of a polymer dissolved in a solvent and a therapeutic substance added thereto is applied to the stent and the solvent is allowed to evaporate. A polymeric coating impregnated with a therapeutic substance then remains on the surface of the stent.
This manufacturing process can consume large quantities of solvent and process time. This process can also reduce the capability of batch processing (e.g., processing large stent quantities in single production runs) since each stent is individually sprayed with or dipped into the coating solution. Accordingly, a stent coating process is desired that reduces waste solvent and process time and can facilitate batch processing.